Alonso took his first podium in seven races in last week's Brazilian Grand Prix after coming out on top of a thrilling battle with Red Bull's Sergio Perez on the last lap.
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With team-mate Lance Stroll fifth, it was a return to form for Aston Martin after impressing with six podiums across the first eight races before fading away into midfield obscurity following the summer break.
Its downturn in performance reached a nadir in the first two races of the Americas triple-header, with Alonso and Stroll eliminated in Q1 at Austin, though Stroll benefited from two disqualifications to grab seventh in the race.
In Mexico, Alonso qualified 13th and Stroll took a pitlane start after qualifying in 18th, before both drivers retired from the race.
Alonso explained that "painful" experiments to find directions for the 2024 car led to the team's worst form of the season.
"I think we've been struggling for a few months, but the last two races were probably quite painful," Alonso said, after securing his eighth podium of the campaign, which has given Aston an outside chance to still beat McLaren for fourth.
"We had to experiment a little bit on a few things on the car to really understand the direction that we were going and we have to go for next year's car as well, so those races were painful, especially Mexico.
Source: Autosport